1. Field of the Invention
The present invention relates to a lead pin with a brazing material fused at a joining surface to a substrate, and in particular, relates to a lead pin with an Au—Ge based brazing material fused at the joining surface.
2. Description of the Related Art
A lead pin which is a conductor member for various electronic components and circuit boards is supplied in the form having a brazing material fused at a head (joining part) of the lead pin, and served for joining components or substrates. A lead pin including a copper-containing alloy such as a copper-iron alloy is typically used, while an Au—Sn (for example, Au-20% by weight of Sn) brazing material is widely used at present as a material for a brazing material. In the manufacture of electronic circuits and electronic equipment, stepwise processes are generally applied, in which assembly of the electronic components or circuit boards are performed by joining lead pins and the like, and then they are assembled by means of soldering. For the stepwise processes, a plurality of brazing materials having different melting points are required. The Au—Sn based brazing material has a melting point of from 280 to 300° C., which is a medium melting point higher than that of the solder (melting point of from 180 to 230° C.) to be used in subsequent assembling processes, and is suitable as a brazing material which will not melt the brazed portion of the components during the assembling process. The Au—Sn based brazing material has been widely used owing to its medium melting point.
The lead pin with a conventional brazing material is manufactured by plating the head of the lead pin with nickel as an undercoat, then plating it with gold, placing the brazing material on top of the gold plating and fusing it. The area for fusing the brazing material is plated with gold, since a eutectic brazing material such as the Au—Sn based brazing material has poor wettablity and poorly flows on a joining surface when melted, so that the flow of the brazing material is improved by the preliminary gold plating on the joining surface in advance.
Application of an Au—Ge based brazing material (Au-12 to 13% by weight of Ge) as a brazing material for the lead pin with a brazing material has recently been studied. This comes from signs of a transition in the kinds of solders used for the manufacture of electronic equipment due to recent concern to environmental issues, that is, a conventional solder (Pb—Sn type) having been replaced by a lead free solder (Sn—Ag type or Sn—Zn type). The lead free solder has a little higher melting point (200 to 300° C.) than a conventional solder, so that use of a brazing material having a higher melting point is considered to be suitable in a joining process of a lead pin, which is an upstream step of soldering. The Au—Ge based brazing material is regarded as a suitable brazing material for a lead pin as it has a melting point of about 360° C. which is a little higher than that of the Au—Sn based brazing material.
The inventors have studied the lead pin in which an Au—Ge based brazing material is fused to the lead pin through a conventional method and found that the joining strength between the brazing material and the lead pin body could not sufficiently be ensured and could result in peeling of the brazing material. The peeling of the brazing material tends to occur by applying impact to the lead pin. Such a low joining strength causes decrease in operation efficiency in the joining of a lead pin, and may cause drop-off of the lead pin from a substrate after the joining.
The present invention has been created under the above background, and it is an object of the present invention to provide a lead pin with an Au—Ge based brazing material in which the brazing material is not peeled even by impact.